Saskia Clark and Hannah Mills, two of Team GB's great hopes for Olympic gold, collapse in fits of giggles as they watch a corny video of them summing each other up in three words. Clark had chosen "quirky, small and hilarious" to describe her boat-mate. Mills went with "tall, fun and old". "Well, you are quite old," the 24-year-old Mills tells Clark, who is eight years her senior. "But wise."

The women make a great double act on and off the water and could be a star turn in Great Britain's sailing team at London 2012. They compete in the women's two-person 470 dinghy class and go into the Olympic regatta at Weymouth and Portland as world champions, the first British women to win the title.

Clark is one of only two women in the British sailing squad with Olympic Games experience, having finished sixth in the 470 class in Beijing. Mills is a newcomer, a graduate of the RYA's junior system and an exciting prospect. The hope is that a string of Olympic medals lies ahead of her. It is early days but she is being spoken of as heir apparent to double gold-medal winners such as Sarah Ayton and Shirley Robertson, and perhaps even the women's answer to the three-times gold‑medal winner Ben Ainslie.

Clark describes her failure to win a medal in 2008 as "heartbreaking". "The feeling was that I didn't give my best performance. I decided I would put that right at London 2012," she has said.

But her bid for Olympic glory in 2012 was initially thwarted by an inability to find the right partner. Among those she trialled with were Ayton and Pippa Wilson, two of the "three blondes in a boat" who won gold in Beijing in the Yngling class and were looking for a new challenge after the class was dropped for London. The partnerships did not work out and it was only in February 2011 that Clark teamed up with Mills.

The pair came to the sport in different ways. Clark grew up in Essex and was introduced to sailing by her father. "I still love bumbling around in creeks, going for barbecues on islands, that sort of thing. That's what I grew up doing." She enjoys returning home and competing with the amateurs she has known since she was a girl: "They love taking a pop at me." She took part in Mersea Week last year, an annual jamboree of sailing and boozing on the Essex coast, and was happy, not to say relieved, to come away with a respectable third place.

Cardiff-born Mills is not from a sailing family but got the bug while on holiday in Cornwall. Back in Wales she found like-minded youngsters and became a fine junior sailor. She is the only Briton to have won the girls' world championship in the Optimist dinghy class.

The two women instantly hit it off. "Sas and I get on well off the water. We enjoy a bit of banter," Mills says. "On the water we totally understand one another." They won silvers in a World Cup event in April 2011 and at the Skandia Sail for Gold regatta at Weymouth and Portland two months later. These were excellent results but not good enough for such an ambitious pair.

"We were a bit worried that silver was all we were worth," says Clark. Then in May this year they won that world championship in Barcelona.

A great strength of the pair is their versatility. They can cope with all sorts of different sea and wind conditions, which will be a bonus during the Olympic regatta. They are hoping it does not blow a gale for the whole of their campaign as they are not the biggest of teams.

"We'd be lying if we didn't say we wanted the gold," Mills says. "But once you're in the thick of it and doing it, you have to focus on turning in your best performance in the Games environment and under pressure. And by the end of the week if we do that we will look at the results and be pleased at where we are."

Spend a little time with the women sailors and it becomes clear they are a close group. During this summer's Sail for Gold regatta in June, Clark and Mills had a disappointing event, squeaking into third place.

But they were whooping and hollering as they returned to the slipway when they heard that Alison Young, the last woman to be picked for the team, had won gold in the single-handed Laser Radial class. The sailors also work hard to make sure the windsurfer Bryony Shaw, who won bronze in Beijing, is not left out. "It's great being part of a solid, tight team," Mills says. "Everyone looks out for one another."

The tabloids may be disappointed at the disappearance of the Yngling class and those "three blondes", Ayton, Wilson and Sarah Webb, none of whom are competing at London 2012. However, all is not lost. The Yngling has been replaced by the women's match-racing event. While the rest of the regatta involves boats competing as a fleet, in match-racing, identical boats race off in one-on-one battles, a simpler contest for the casual sailing spectator to watch. You need skill in abundance but the event is also about bravery and nerve.

After Beijing, Annie Lush and Lucy Macgregor established themselves as the leading British crew and helm in the match-racing class. Lucy's little sister, 21-year-old Kate – "Mini Mac" – was studying business at Southampton Solent University and helping Lucy and Lush train. But at the start of 2011 Kate was persuaded to join the match-racing team as full-time bow. The combination worked immediately and the three are one of the best match-racing teams in the world. The dynamics of a pair of sisters and one other taking part in such a form of racing is fascinating. But Lush is not left out.

"We're very much a team," she says. It helps that all three grew up in Poole. "I've known them both forever. We all have homes in Poole. I can almost see Kate's flat from my house. Lucy is half a mile away.

"I've probably spent as much time with Lucy as Kate has over the last six years. But having Kate join has worked well. It was important to have someone come in who felt part of the team at once and not have the two-on-one situation that happens a lot on three-person teams."

Naturally, teamwork is key. The Elliott 6m that is used in match-racing is a relatively large boat that ideally would be sailed by four people. It means crews are, effectively, short-handed. Lucy controls the tiller while Kate, the most nimble, dodges around the front of the boat and spots the breeze.

Lush, six inches taller than the other two, is positioned in the middle and does much of the hard hauling. Races develop and change quickly. At different times all three take turns in calling moves and tactics.

Lucy says taking her kid sister on saved a lot of time for the team. "It's important to be able to judge people's personalities, when you need to push them further, when you need to back off. It can take up to two years to bond; with us it happened very quickly."

According to Kate, once they are on the water the sisters do not think of their relationship. There is no petty squabbling. "We don't think about the fact we're sisters. We try to keep the sister and the professional relationship separate."

The match-racing women are hoping that the spectator-friendly format will lead to them being roared on to victory. They have been picturing spectators packed into the ticketed viewing area at Nothe Fort in Weymouth. "When we've been out there sailing I've been having a look at the Nothe Fort and trying to visualise people with flags," says Lush. "It will be cool to hear them shouting for us."